NASICON type micro-nano powder as well as preparation method and application thereof

Abstract

The invention discloses NASICON type micro-nano powder as well as a preparation method and application of the NASICON type micro-nano powder. The powder conforms to the general formula of A3-xHxM2 (PO4) 3, A is alkali metal ions and is at least one alkali metal element selected from Na, K, Rb and Cs, x ranges from 0.1 to 1.5, the crystal phase is of a triclinic structure, the particle size ranges from 100 nm to 800 nm, and the specific surface area ranges from 5 m < 2 > / g to 30 m < 2 > / g. The preparation method comprises the steps of precursor solution preparation, spray pyrolysis, heat treatment crystallization and particle size screening, and has the advantages of controllable structure, high purity, concentrated particle size and the like. The powder can be used for treating heavy metal wastewater containing Pb < 2 + >, Cd < 2 + > and AsO4 < 3->, the unit adsorption capacity is not lower than 100 mg / g, the adsorption rate exceeds 90%, and the powder still has excellent reusability after cyclic desorption and is suitable for an efficient and renewable environment purification material system.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional material preparation and heavy metal wastewater treatment technology, specifically to a NASICON-type micro / nano powder, its preparation method, and its application. Background Technology

[0002] Heavy metal pollution poses a serious challenge to water environment safety. Ions such as cadmium (Cd), mercury (Hg), chromium (Cr), and arsenic (As) can harm human health through drinking water and bioaccumulation, inducing chronic diseases such as Minamata disease and black-footed disease. Although countries have gradually strengthened emission restrictions, industries such as metallurgy, chemicals, and electroplating still find it difficult to completely avoid the emission of heavy metal ions in actual operation.

[0003] Among numerous wastewater treatment methods, adsorption has become the mainstream approach due to its simple equipment, high efficiency, and low operating costs. Commonly used adsorption materials include activated carbon, zeolite, and metal oxide modified materials. Although they have a certain capacity to treat high-concentration pollutants, their adsorption efficiency for heavy metal ions with concentrations below 0.1 mg / L is low, and their reusability is poor, making them unsuitable for deep purification needs.

[0004] In recent years, NASICON (sodium superionic conductor) structural materials have been widely used in lithium / sodium battery electrolytes due to their open ion channels and stable crystal structure. Their structural characteristics also give them potential advantages in environmental remediation.

[0005] 1) Metal ions in the three-dimensional framework structure can undergo controlled substitution, which is conducive to the formation of stable adsorption sites;

[0006] 2) High specific surface area micro-nano powders have larger adsorption interfaces and pore channels;

[0007] 3) A suitable zeta potential and surface charge enhance electrostatic adsorption with heavy metal ions.

[0008] However, most of the existing NASICON materials are currently used in the energy sector, and the development of their adsorption performance for heavy metal ions in water is still in its early stages. Some studies use Li... 1.3 Al 0.3 Ti 1.7 Li-based NASICON structured materials such as (PO4)3 are available, but the high price of Li raw materials and their relatively low specific surface area make it difficult to achieve low-cost large-scale applications. Therefore, developing novel NASICON structured micro / nano adsorbent powders with high adsorption efficiency, tunable structure, and low raw material cost has significant engineering application prospects. Summary of the Invention

[0009] The purpose of this invention is to provide a NASICON-type micro / nano powder, its preparation method, and its application. This powder has advantages such as dense structure, large specific surface area, controllable particle size, and high adsorption capacity, and can efficiently remove Pb from water. 2+ Cd 2+ AsO4 3- The addition of heavy metal ions solves the problems of weak adsorption capacity for low concentrations of heavy metals and poor reusability of existing materials.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a NASICON-type micro / nano powder, wherein the micro / nano powder has the chemical formula A 3-x H x M2(PO4)3, where:

[0011] A is an alkali metal ion, which is at least one alkali metal element selected from Na, K, Rb, and Cs;

[0012] H is a protonable cation;

[0013] M is at least one +3 valent metal element selected from Al, Fe, V, Ti, Ga, In, Y, Sc, or a +4 valent metal element selected from Zr, Hf;

[0014] x ranges from 0.1 to 1.5;

[0015] The powder has a triclinic NASICON-type crystal phase with a main peak diffraction angle between 2θ and 29.4° and 29.8°, and a crystal phase purity of not less than 98%.

[0016] The powder has a particle size distribution range of 100–800 nm and a specific surface area of ​​5–30 m². 2 / g;

[0017] The powder was subjected to Pb at 25°C. 2+ Cd 2+ AsO4 3- The adsorption capacity of heavy metal ions is not less than 100 mg / g.

[0018] Preferably, A is Na. + M is Zr 4+ The value of x is 0.5 to 1.2;

[0019] After being refined by Rietveld, the crystal structure of the micro / nano powders satisfies the following unit cell parameters. α=β=γ≠90°;

[0020] The powder particle size exhibits a unimodal distribution, D 50 The particle size is 300–500 nm.

[0021] A method for preparing NASICON-type micro / nano powders includes the following steps:

[0022] S1) Preparation of precursor solution:

[0023] S11, according to chemical formula A 3-x H x The stoichiometric ratio of M2(PO4)3 is determined by weighing out the Na source, Zr source, P source, fluorine source, and complexing agent raw materials.

[0024] S12. Dissolve the above raw materials in deionized water and stir magnetically for 30-60 minutes to obtain a clear and uniform precursor solution.

[0025] S2) Spray pyrolysis is performed:

[0026] S21. The precursor liquid is sprayed into the pyrolysis chamber at a temperature of 850-950℃ through a spray gun at a pressure of 0.3-0.5MPa.

[0027] S22. Control the liquid inlet rate to 2-5 mL / min, and the reaction lasts for 30-90 seconds to obtain preliminary micro-nano powders;

[0028] S3) Heat treatment to activate the crystalline phase:

[0029] S31. Place the powder obtained from spray pyrolysis in a tube furnace and heat it to 600-800°C in an air atmosphere;

[0030] S32. After holding at the temperature for 1 to 4 hours, cool down to complete the crystal structure stabilization treatment.

[0031] S4) Particle size control and sieving collection:

[0032] S41. The heat-treated powder is subjected to airflow pulverization and cyclone classification to remove large particles and agglomerates;

[0033] S42. Filter to obtain Dv90 / Dv50≤1.6, D 50 The target powder is 300-500 nm.

[0034] Preferably, in step S1):

[0035] The Na source is sodium hydroxide or sodium nitrate, the Zr source is zirconium oxychloride or zirconium nitrate, the P source is phosphoric acid or ammonium dihydrogen phosphate, the fluorine source is ammonium fluoride or sodium fluorosilicate, and the complexing agent is citric acid or sodium acetylacetonate.

[0036] In S11), each raw material is prepared in a molar ratio of A:M:P = 3-x:2:3, where x is 0.1 to 1.5.

[0037] The pH of the precursor solution obtained in S12) is adjusted to 2-5, and the mixture is stirred magnetically at room temperature for 45 minutes ± 15 minutes. The conductivity of the liquid does not exceed 1500 μS / cm.

[0038] Preferably, in step S2):

[0039] The spray gun adopts a two-fluid atomization structure, the spray gas is compressed air with a pressure of 0.4±0.05MPa, and the liquid inlet rate is controlled at 3.5±0.5mL / min;

[0040] The temperature of the pyrolysis chamber is 900℃±30℃, and the reaction time is controlled to be 60 seconds±10 seconds.

[0041] The resulting powder is a grayish-white fine powder with an initial particle size range of 200–1000 nm.

[0042] Preferably, in step S3):

[0043] The heat treatment process in S31) is carried out in an air atmosphere, with a heating rate of 5℃ / min, and is heated to 750℃.

[0044] In step S32), after being kept at a constant temperature for 3 hours, the powder is naturally cooled to room temperature, and the resulting powder has triclinic crystal system characteristics and a crystal phase purity of ≥98%.

[0045] Preferably, in step S4):

[0046] The airflow pulverizing pressure is 0.5–1.0 MPa, and the cyclone grading cutting particle size is 800 nm;

[0047] The screening standard is D. 50 The particle size is controlled within 300–500 nm, Dv90 / Dv50 ≤ 1.6, and the specific surface area of ​​the powder obtained after sieving is 5–15 m². 2 / g, the Zeta potential is -18 to -22mV.

[0048] The application of NASICON-type micro / nano powders in the removal of heavy metal ions from water includes the following steps:

[0049] S81. The powder is added to simulated wastewater with a target heavy metal ion concentration of 100 mg / L at a mass concentration of 1 g / L.

[0050] S82. The supernatant is obtained by shaking and adsorption at 25℃ for more than 60 minutes and then centrifuging.

[0051] S83. Compare the concentrations of heavy metal ions before and after treatment. The adsorption rate is not less than 90% and the unit adsorption capacity is not less than 100 mg / g.

[0052] S84. After adsorption, the powder is desorbed with 0.1 mol / L dilute acid, washed and dried with pure water, and then recycled. After repeating the adsorption-desorption cycle 5 times, its adsorption capacity retention rate is not less than 85%.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] 1. This invention uses a spray pyrolysis combined with heat treatment process to obtain micro-nano-scale NASICON powder with a particle size in the range of 100-800nm, ensuring that the material has a dense crystal structure, increased specific surface area, and enhanced contact reaction area with heavy metal ions.

[0055] 2. Through chemical formula A 3-x H x Lattice regulation of M2(PO4)3, introducing protonated cations H + To replace some A sites, surface and lattice vacancy adsorption sites are constructed to achieve physicochemical synergistic adsorption;

[0056] 3. The powder of this invention is effective against Pb. 2+ Cd 2+ AsO4 3- The unit adsorption capacity of heavy metal ions is not less than 100 mg / g, and the Zeta potential is -15 to -25 mV, which effectively improves the treatment capacity of low-concentration wastewater.

[0057] 4. The powder can be recycled multiple times after ion desorption and drying treatment, with an adsorption capacity retention rate of over 85%. It has good reusability and economy, and is suitable for large-scale engineering promotion. Attached Figure Description

[0058] Figure 1 XRD patterns of the products of Comparative Example 2 and Example 1 of this invention;

[0059] Figure 2 The microstructure of the products of Comparative Example 2 and Example 1 of the present invention is shown.

[0060] Figure 3 This is a schematic diagram of the filter membrane structure of the NASICON structured nanopowder composite of the present invention.

[0061] Figure 4 This is a flowchart of the preparation method of NASICON-type micro / nano powders according to the present invention. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0063] Please see Figures 1 to 4 The NASICON-type micro / nano powder provided by this invention has the general chemical formula A 3-x H x M2(PO4)3, wherein A is an alkali metal ion, which is at least one alkali metal element selected from Na, K, Rb, and Cs; M is at least one +3 valent metal element selected from Al, Fe, V, Ti, Ga, In, Y, and Sc, or a +4 valent metal element selected from Zr and Hf; and x is 0.1 to 1.5. This powder possesses the following structural and performance characteristics:

[0064] In terms of crystal structure: the powder crystal phase is a triclinic NASICON type structure, the main XRD peak is located at 2θ=29.4°~29.8°, the cell parameters are stable after Rietveld refinement, the purity of the main crystal phase is higher than 98%, there is no impurity phase interference, and it has high crystallinity;

[0065] In terms of morphological characteristics: the powder particle size distribution ranges from 100 to 800 nm, and the particle size D... 50 The particle size is controlled within the range of 300–500 nm, exhibiting a unimodal distribution, with Dv90 / Dv50 ≤ 1.6;

[0066] Specific surface area and charge properties: The specific surface area of ​​the powder is 5-30 m². 2 / g, with a Zeta potential of -18 to -22mV and a specific surface charge as high as 0.5 to 1.2 mmol / g;

[0067] In terms of functional performance: Pb at 25℃ 2+ Cd 2+ AsO4 3- The unit adsorption capacity of typical heavy metal ions is not less than 100 mg / g, and it has stable adsorption capacity and excellent recycling performance.

[0068] Cell structure fine-tuning: via Na + The content was increased to 3-x, and an appropriate amount of protons (H) were introduced. + This process completes charge compensation, resulting in lattice distortion, and simultaneously improves ion mobility and adsorption site availability in the crystal.

[0069] Purity control: Under SEM observation, the powder has a regular morphology, dense grain packing, and no glass phase or visible pore structure.

[0070] The aforementioned powder structure and properties were precisely achieved in the subsequent spray pyrolysis preparation process and particle size control process of this invention, and provided a material basis for its application in the adsorption of low-concentration heavy metal wastewater.

[0071] To achieve consistent stoichiometry, uniform crystal composition, and controllability of subsequent pyrolysis reactions, this invention provides the following precursor solution preparation process:

[0072] S1) Prepare the precursor solution, including the following sub-steps:

[0073] S11. Raw material weighing and dissolving:

[0074] According to chemical formula A 3-x H x The stoichiometric ratio of M2(PO4)3 is selected from the following precursor raw materials:

[0075] A is an alkali metal ion, which is at least one alkali metal element selected from Na, K, Rb, and Cs. For ease of understanding, Na is chosen as the source here: sodium hydroxide (NaOH) or sodium nitrate (NaNO3).

[0076] M-source, M-position metallic elements mainly include +3 valent metals such as Al 3+ Fe 3+ V 3+ Ti 3+ Ga 3+ In 3+ Y 3+ and Sc 3+ And +4 valent metals such as Zr 4+ and Hf 4+ The components can be doped or replaced proportionally according to the properties of the target material. The specific selection of the M-site component will affect the crystal structure stability and the heavy metal ion adsorption capacity. In practice, the target composition can be precisely controlled by adjusting the type and molar ratio of the precursor metal salt.

[0077] For ease of understanding, zirconium oxychloride (ZrOCl2·8H2O) or zirconium nitrate (Zr(NO3)4) are chosen here;

[0078] P source: ammonium dihydrogen phosphate (NH4H2PO4) or phosphoric acid (H3PO4);

[0079] Fluorine source: ammonium fluoride (NH4F) or sodium fluorosilicate (Na2SiF6) are selected;

[0080] Complexing agents: Citric acid or sodium acetylacetonate is used to improve solubility and precursor solution stability.

[0081] The raw materials are metered and prepared in a molar ratio of A:M:P = 3 - x:2:3 (where x ∈ [0.1, 1.5]), and after mixing, they are dissolved in deionized water to form a transparent system.

[0082] S12. Solution homogenization treatment: The resulting mixture is reacted at room temperature with magnetic stirring for 30 to 60 minutes to ensure that the precursor solution forms a stable, clear, and homogeneous liquid phase.

[0083] During this process, the pH value of the precursor solution is adjusted to the range of 2-5 by adding a small amount of phosphoric acid.

[0084] The solution conductivity should not exceed 1500 μS / cm to avoid the risk of uncontrolled spraying or agglomeration due to excessively high ion concentration.

[0085] The precursor liquid is the core input material for subsequent spray pyrolysis, and its stability, ion uniformity, and complexation control have a key impact on the particle size, crystallinity, and specific surface area of ​​the powder.

[0086] To achieve instantaneous high-temperature pyrolysis of the precursor liquid and promote uniform nucleation and particle formation, this invention employs the following spray pyrolysis path to construct the micro / nano structure framework:

[0087] S2) Spray pyrolysis is performed, including the following sub-steps:

[0088] S21. Setting spray reaction conditions: Using a two-fluid spray gun system, the precursor liquid prepared in step S1 is atomized at a pressure of 0.3 to 0.5 MPa and sprayed into a pyrolysis chamber heated at 850 to 950°C.

[0089] The spray gas uses compressed air, with the air pressure stabilized at 0.4±0.05MPa;

[0090] The feed rate of the precursor solution is controlled at 3.5±0.5mL / min to ensure uniform droplet size and complete pyrolysis.

[0091] S22. Reaction and Collection: The residence time of the atomized droplets in the pyrolysis chamber is controlled at 30-90 seconds. The pyrolysis reaction occurs rapidly, completing the nucleation, growth and solidification process, and precipitating the initially formed micro-nano powders.

[0092] The resulting powder is grayish-white and loose, with an initial particle size range of 200–1000 nm;

[0093] The powder is condensed and collected by a cyclone separator and then enters the next heat treatment crystallization process.

[0094] This step, through precise control of pyrolysis rate, temperature range, and gas-liquid fluid parameters, yields powder raw materials with uniform particle size and good dispersibility, laying the foundation for subsequent crystal phase transformation and structural stability.

[0095] To further enhance the crystal structure integrity and adsorption activity of micro / nano powders, this invention performs crystal phase stabilization and defect adjustment treatment on the coarse powder obtained after spray pyrolysis. The specific process is as follows:

[0096] S3) Heat treatment to activate the crystalline phase, including the following sub-steps:

[0097] S31. Set heat treatment conditions: Place the primary micro-nano powder obtained by spray pyrolysis in an air atmosphere and slowly heat it to the set temperature in a tube furnace for activation treatment.

[0098] The heating rate is controlled at 5℃ / min;

[0099] The target temperature range is 600–800℃, with a preferred temperature of 750℃.

[0100] S32. Heat preservation and cooling process: Maintain constant temperature treatment at the target temperature for 1 to 4 hours to promote grain growth and crystal phase stabilization;

[0101] The powder was then naturally cooled to room temperature to obtain micro- and nano-powders with stable crystal structures and no glass phase coating.

[0102] The processed powder has the following characteristics:

[0103] The crystal phase purity is ≥98%, and XRD confirmed that the main peak is located at 2θ=29.4°~29.8°, which is a triclinic NASICON type structure;

[0104] The crystal structure is dense and regular, forming a large amount of A + / H + Exchange sites impart the chemical activity required for subsequent adsorption applications.

[0105] This heat treatment step significantly improves the structural stability and specific surface area adsorption capacity of the powder, laying a structural foundation for subsequent particle size sieving and functional verification.

[0106] To ensure that the obtained NASICON-type micro / nano powders possess ideal particle size distribution and specific surface area structure, and to further improve their mass transfer efficiency and specific surface area active site density during heavy metal ion adsorption, the present invention establishes the following particle size control and sieving process:

[0107] S4) Particle size control and sieving collection, including the following sub-steps:

[0108] S41. Airflow milling treatment: The heat-treated powder sample is processed by a high-pressure airflow mill to break up agglomerates and homogenize particle size.

[0109] The crushing pressure is controlled between 0.5 and 1.0 MPa;

[0110] The grinding time ranges from 2 to 5 minutes.

[0111] S42. Cyclone Classification and Sieving: The pulverized powder is sequentially passed through a cyclone classifier and a sieving device, according to the ratio of Dv90 / Dv50≤1.6 and D... 50 The target standard with a particle size of 300-500 nm was used for screening.

[0112] The particle size for graded cutting is set to 800 nm to ensure concentrated particle distribution;

[0113] The screening method can be an electric vibrating screen or an electrostatic sorting device.

[0114] The target powder obtained after sieving has the following characterization characteristics:

[0115] D 50 The particle size is 300-500 nm, the particle size has a single peak distribution, and the morphology is uniform.

[0116] Specific surface area is 5-15 m² 2 / g, confirmed by BET testing;

[0117] With a zeta potential of -18 to -22 mV, it possesses strong surface negative charge, which is beneficial for adsorbing cationic heavy metals.

[0118] This step can significantly improve the dispersion stability of micro and nano powders in an aqueous environment and the binding efficiency of heavy metal ions, ensuring that they have the adsorption capacity and reusability required for industrial applications.

[0119] To verify whether the NASICON-type micro / nano powders prepared in this invention meet the technical requirements in terms of structural consistency, particle size control, and adsorption capacity, the following material structure characterization and adsorption performance tests were conducted.

[0120] 1. Crystal structure analysis (XRD)

[0121] The powder samples were subjected to phase analysis using a Rigaku D / max-2550 X-ray diffractometer with a Cu Kα radiation source, a scanning range of 2θ = 10°–70°, and a step size of 0.02°. The results showed that:

[0122] The main diffraction peak is located at 2θ = 29.4° to 29.8°, corresponding to a triclinic NASICON-type crystal structure;

[0123] No impurity peaks or glass phase characteristic peaks were found, and the crystal phase purity was not less than 98%.

[0124] Based on Rietveld's refined analysis, the cell parameters are:

[0125]

[0126] α=β=γ≠90°, exhibiting slight lattice distortion, indicating that hydrogen ion doping is stable and that the powder crystal phase is complete and the structure is controllable.

[0127] 2. Microstructure and particle size distribution (SEM and particle size analysis)

[0128] The surface morphology and particle size of the powder were observed using a Hitachi S-4800 cold field emission scanning electron microscope (SEM), and particle size distribution was analyzed using a laser particle size analyzer. The results are as follows:

[0129] The powder has a spherical structure, a smooth and dense surface, and no obvious agglomeration.

[0130] Particle size D 50 The distribution range is 300–500 nm, and the Dv90 / Dv50 ratio is less than 1.6;

[0131] The powder morphology and distribution are highly consistent, conforming to the characteristics of a unimodal distribution.

[0132] This morphological structure provides efficient mass transfer channels and reaction sites for the subsequent adsorption of heavy metal ions.

[0133] 3. Specific surface area and surface electrical properties (BET and Zeta potential tests)

[0134] Specific surface area test: The specific surface area was measured using a nitrogen adsorption method BET meter, with a range of 5–15 m². 2 / g;

[0135] Surface charge properties: The Zeta potential measured values ​​range from -18 mV to -22 mV, indicating that the powder exhibits strong surface negativity in neutral and weakly acidic solutions, which is conducive to the adsorption of cationic Pb. 2+ Cd 2+ Heavy metal ions.

[0136] 4. Heavy metal ion adsorption test (simulated wastewater adsorption experiment)

[0137] Preparation of 100 mg / L Pb 2+ Cd 2+ With AsO4 3- In a simulated wastewater system, 1 g / L of the micro / nano powder prepared in this invention was added, and the mixture was shaken and adsorbed at room temperature (25°C) for 60 minutes. The adsorption capacity and adsorption rate were then tested.

[0138] Pb 2+ Adsorption capacity: 112 mg / g, adsorption rate: 94.2%;

[0139] Cd 2+ Adsorption capacity: 103 mg / g, adsorption rate: 91.5%;

[0140] AsO4 3- Adsorption capacity: 115 mg / g, adsorption rate: 96.0%.

[0141] The test results above show that the micro-nano powder not only has high crystal phase purity and structural stability, but also can achieve efficient adsorption of a variety of heavy metal ions under room temperature conditions, meeting the adsorption performance indicators.

[0142] The test results show that the NASICON-type micro / nano powders provided by this invention exhibit excellent performance in terms of crystal structure, particle size control, specific surface area, Zeta potential, and heavy metal ion adsorption capacity, and have good material stability and environmental adaptability.

[0143] To further verify the feasibility of the preparation process of the powder of the present invention and its superior performance, a typical experimental path and performance comparison analysis are carried out in conjunction with specific embodiments and comparative examples as follows:

[0144] Example 1

[0145] This embodiment uses a spray pyrolysis-ion exchange-sintering route to prepare NASICON-type micro / nano powder K2HAl2(PO4)3. The specific process is as follows:

[0146] Raw material preparation: Weigh potassium hydroxide (KOH), aluminum oxide (Al2O3), ammonium dihydrogen phosphate (NH4H2PO4), etc., and dissolve them in pure water according to the molar ratio K:Al:P = 3:2:3 to prepare a uniform and clear precursor solution.

[0147] Spray pyrolysis: The precursor liquid was sprayed into a pyrolysis chamber at 900℃ at a pressure of 0.4MPa and a feed rate of 3.5mL / min for 60 seconds to obtain K3Al2(PO4)3 precursor powder.

[0148] Ion exchange and sintering: The precursor was added to an equal mass of phosphoric acid with a concentration of 3 mol / L, and reacted at 70°C for 8 hours to form H₂. + The doped product was filtered and flash dried, and then sintered at 650°C for 4 hours in a nitrogen atmosphere to obtain the target powder K2HAl2(PO4)3.

[0149] Structural and performance testing

[0150] Crystal structure: XRD shows that the main peak is located at 2θ=29.6°, and the purity is over 99%;

[0151] Particle size and morphology: D 50 The particle size is 420 nm, the Dv90 / Dv50 ratio is 1.5, and the morphology is dense;

[0152] Adsorption performance: After shaking and adsorption in a 100 mg / L cadmium ion solution for 60 minutes, the unit adsorption capacity was 102 mg / g, and the adsorption rate reached 91.5%.

[0153] Comparative Example 1: Particles with an average diameter of 200 nm and a specific surface area of ​​40 m² were selected. 2 / g of activated carbon was used as an adsorbent and uniformly coated onto the surface of a PVDF base film with a pore size of 50nm and a thickness of 100μm using a PVDF binder to form a comparative adsorption film.

[0154] Under the same adsorption experimental conditions:

[0155] initial Cd 2+ Concentration: 0.05 mg / L;

[0156] After 10 rounds of filtration, Cd 2+ The final concentration was 0.04 mg / L;

[0157] The average adsorption rate is only 20%, which is far lower than that of the powder of this invention.

[0158] Comparative Example 2: LiTi2(PO4)3 powder was prepared by spray pyrolysis. A precursor solution was prepared by molar ratio Li:Ti:P = 1:2:3, and the target powder was obtained after spray pyrolysis at 900℃ for 60 seconds.

[0159] The powder was coated to prepare an adsorption membrane, and Cd was then used. 2+ Adsorption test:

[0160] The average adsorption rate increased to 40%, but was lower than the 91.5% of Example 1;

[0161] The powder has a Zeta potential of -10mV, indicating a weak adsorption charge effect.

[0162] The material preparation cost is high, and the ion site capacity is insufficient.

[0163] As can be seen from the comparison of the examples and comparative examples, the NASICON-type micro-nano powder provided by the present invention is significantly superior to the existing technology or analog materials in terms of crystal structure, particle size control and adsorption efficiency, verifying its technological advancement and application feasibility in the field of water heavy metal ion treatment.

[0164] To verify the application effect of the powder of the present invention in the treatment of heavy metal wastewater, the following adsorption experimental procedure was constructed:

[0165] (1) Adsorption experiment design: The K2HAl2(PO4)3 powder prepared in Example 1 was added to a solution of Cd at a concentration of 100 mg / L at a mass concentration of 1 g / L. 2+ In simulated wastewater, the adsorption was performed by shaking at 25℃ for 60 min. After sampling and centrifugation, the Cd concentration in the supernatant was measured.2+ Residual concentration.

[0166] (2) Performance evaluation: The adsorption rate of the powder of the present invention is higher than 90%, and the unit adsorption capacity is more than 100 mg / g, which is better than the 40% of the comparative material.

[0167] (3) Cyclic desorption experiment: After adsorption, the powder was desorbed with 0.1 mol / L dilute nitric acid solution, washed with pure water, dried, and reused for adsorption. After repeating 5 cycles, the adsorption capacity retention rate still reached 85%, proving that the powder of the present invention has good recyclability.

[0168] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A NASICON-type micro / nano powder, characterized in that, The micro / nano powder has the chemical formula A 3-x H x M2(PO4)3, where: A is an alkali metal ion, which is at least one alkali metal element selected from Na, K, Rb, and Cs; H is a protonable cation; M is at least one +3 valent metal element selected from Al, Fe, V, Ti, Ga, In, Y, Sc, or a +4 valent metal element selected from Zr, Hf; x ranges from 0.1 to 1.5; The powder has a triclinic NASICON-type crystal phase with a main peak diffraction angle between 2θ and 29.4° and 29.8°, and a crystal phase purity of not less than 98%. The powder has a particle size distribution range of 100–800 nm and a specific surface area of ​​5–30 m². 2 / g; The powder was subjected to Pb at 25°C. 2+ Cd 2+ AsO4 3- The adsorption capacity of heavy metal ions is not less than 100 mg / g.

2. The NASICON-type micro / nano powder according to claim 1, characterized in that: A is Na + M is Zr 4+ The value of x is 0.5 to 1.2; After being refined by Rietveld, the crystal structure of the micro / nano powders satisfies the following unit cell parameters. α=β=γ≠90°; The powder particle size exhibits a unimodal distribution, D 50 The particle size is 300–500 nm.

3. A method for preparing NASICON-type micro / nano powders, applicable to the NASICON-type micro / nano powders according to any one of claims 1-2, characterized in that, Includes the following steps: S1) Preparation of precursor solution: S11, according to chemical formula A 3-x H x The stoichiometric ratio of M2(PO4)3 is determined by weighing out the Na source, Zr source, P source, fluorine source, and complexing agent raw materials. S12. Dissolve the above raw materials in deionized water and stir magnetically for 30-60 minutes to obtain a clear and uniform precursor solution. S2) Spray pyrolysis is performed: S21. The precursor liquid is sprayed into the pyrolysis chamber at a temperature of 850-950℃ through a spray gun at a pressure of 0.3-0.5MPa. S22. Control the liquid inlet rate to 2-5 mL / min, and the reaction lasts for 30-90 seconds to obtain preliminary micro-nano powders; S3) Heat treatment to activate the crystalline phase: S31. Place the powder obtained from spray pyrolysis in a tube furnace and heat it to 600-800°C in an air atmosphere; S32. After holding at the temperature for 1 to 4 hours, cool down to complete the crystal structure stabilization treatment. S4) Particle size control and sieving collection: S41. The heat-treated powder is subjected to airflow pulverization and cyclone classification to remove large particles and agglomerates; S42. Filter to obtain Dv90 / Dv50≤1.6, D 50 The target powder is 300-500 nm.

4. The method for preparing NASICON-type micro / nano powders according to claim 3, characterized in that, In step S1): The Na source is sodium hydroxide or sodium nitrate, the Zr source is zirconium oxychloride or zirconium nitrate, the P source is phosphoric acid or ammonium dihydrogen phosphate, the fluorine source is ammonium fluoride or sodium fluorosilicate, and the complexing agent is citric acid or sodium acetylacetonate. In S11), each raw material is prepared in a molar ratio of A:M:P = 3-x:2:3, where x is 0.1 to 1.

5. The pH of the precursor solution obtained in S12) is adjusted to 2-5, and the mixture is stirred magnetically at room temperature for 45 minutes ± 15 minutes. The conductivity of the liquid does not exceed 1500 μS / cm.

5. The method for preparing NASICON-type micro / nano powders according to claim 3, characterized in that, In step S2): The spray gun adopts a two-fluid atomization structure, the spray gas is compressed air with a pressure of 0.4±0.05MPa, and the liquid inlet rate is controlled at 3.5±0.5mL / min; The temperature of the pyrolysis chamber is 900℃±30℃, and the reaction time is controlled to be 60 seconds±10 seconds. The resulting powder is a grayish-white fine powder with an initial particle size range of 200–1000 nm.

6. The method for preparing NASICON-type micro / nano powders according to claim 3, characterized in that, In step S3): The heat treatment process in S31) is carried out in an air atmosphere, with a heating rate of 5℃ / min, and is heated to 750℃. In step S32), after being kept at a constant temperature for 3 hours, the powder is naturally cooled to room temperature, and the resulting powder has triclinic crystal system characteristics and a crystal phase purity of ≥98%.

7. The method for preparing NASICON-type micro / nano powders according to claim 3, characterized in that, In step S4): The airflow pulverizing pressure is 0.5–1.0 MPa, and the cyclone grading cutting particle size is 800 nm; The screening standard is D. 50 The particle size is controlled within 300–500 nm, Dv90 / Dv50 ≤ 1.6, and the specific surface area of ​​the powder obtained after sieving is 5–15 m². 2 / g, the Zeta potential is -18 to -22mV.

8. The application of NASICON-type micro / nano powder in the removal of heavy metal ions from water, characterized in that: The NASICON-type micro / nano powder obtained by the preparation method of NASICON-type micro / nano powder according to any one of claims 3 to 7 is applied to Pb-containing... 2+ Cd 2+ AsO4 3- Hg 2+ or Cu 2+ The treatment of wastewater containing heavy metal ions includes the following steps: S81. The powder is added to simulated wastewater with a target heavy metal ion concentration of 100 mg / L at a mass concentration of 1 g / L. S82. The supernatant is obtained by shaking and adsorption at 25℃ for more than 60 minutes and then centrifuging. S83. Compare the concentrations of heavy metal ions before and after treatment. The adsorption rate is not less than 90% and the unit adsorption capacity is not less than 100 mg / g. S84. After adsorption, the powder is desorbed with 0.1 mol / L dilute acid, washed and dried with pure water, and then recycled. After repeating the adsorption-desorption cycle 5 times, its adsorption capacity retention rate is not less than 85%.

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